Press-actuation system

ABSTRACT

A press has upper and lower dies, an actuating element spaced vertically from one of the dies, and a platen carrying the one die and between the element and the one die. A membrane defines a closed chamber having one side operatively bearing vertically on the platen and an opposite side bearing vertically on the element. A fluid supply pressurizes the chamber and maintains in the chamber a predetermined pressure. An actuator connected to the element vertically displaces the element, platen, and one die.

FIELD OF THE INVENTION

The present invention relates to pres. More particularly this inventionconcerns an actuation system for a press.

BACKGROUND OF THE INVENTION

A typical press used, for example, in a packing machine to laminatetogether two plastic foils has an upper die and a lower die, normallyheated. Typically the upper die has a planar lower face and the lowerdie has a planar upper face formed with an array of upwardly openpockets. A planar upper foil and a lower foil formed with an array ofupwardly open product-containing blisters are passed horizontallythrough the press. The two dies are pressed together between advancesteps of the foils when the blisters are aligned with the pockets in thelower die to laminate the two foils together between the blisters. Suchsystems are described in German patent documents 197 40 988 and 74 05441 and in U.S. Pat. No. 5,105,603.

The two dies are relatively large and quite massive, and the foils arequite thin and are formed of a moderately fragile plastic. It istherefore essential that the dies be moved together with enormousprecision so as to press the foils together with just enough force thatthey bond together, but not so much that they extrude out or aredamaged.

Obviously the problem here is that any slight misalignment can result ina spoiled workpiece. If the two foils are not solidly bonded together,the resultant package is unusable. Similarly if the two foils arepinched excessively, there will be weak spots or holes that also resultin an unusable finished product.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide animproved press-actuation system.

Another object is the provision of such an improved press-actuationsystem that overcomes the above-given disadvantages, in particular thatensures that the pressure exerted on the foils will be uniform andaccurately controlled.

SUMMARY OF THE INVENTION

A press has according to the invention upper and lower dies, anactuating element spaced vertically from one of the dies, and a platencarrying the one die and between the element and the one die. A membranedefines a closed chamber having one side operatively bearing verticallyon the platen and an opposite side bearing vertically on the element. Afluid supply pressurizes the chamber and maintains in the chamber apredetermined pressure. An actuator connected to the element verticallydisplaces the element, platen, and one die.

Thus with this system the pressurizable chamber provided between theactuator and the one die limits the maximum pressure the one die canapply to the workpiece. If the actuator, which is typically a powerfulhydraulic cylinder or motor, moves the element somewhat too far, thechamber will simply deform and the pressure transmitted to the workpiecewill be that in the chamber. In addition if one of the dies is slightlycanted, that is nonparallel, to the other die, the chamber will deformto allow them to move parallel without pinching or overly compressingthe workpiece. What is more, the actuator can be set to perform a simplelifting stroke and any adjustment or fine-tuning of the closing pressureis handled by the supply system connected to the force-transmittingchamber.

What is more, the chamber ensures that the force of the press actuator,which typically is applied at one or more separate locations to theactuating element, is distributed over the entire platen. Thus even ifthe element deforms, the platen will be applied smoothly and flatly.

According to the invention the platen and element together form acompartment holding the membrane. The platen is provided with guide barsin which the element is vertically slidable, and/or the platen is formedwith a cavity open toward the element and holding the membrane and inwhich the actuating element is slidable. The cavity receives themembrane with some play, that is lateral spacing, so it can spread anddeform as needed.

The supply system pressurizes the chamber with a gas, normally air. Thismakes it possible to control the workpiece-clamping pressure accuratelyand very easily. What is more, such a pneumatic system isenvironmentally friendly as compared, for example, to a oil-filledhydraulic system, as any leakage does not create a problem and, ifminor, does not even require shutting down the press.

The membrane according to the invention forms a bladder. It can haveseveral compartments for local control of pressure, or be formed as astack of compartments. The bladder can easily be exchanged or replaced.When multiple bladders are used, they can be switched out to achievedifferent pressures in different areas, and generally provide localpressure control.

The press further has according to the invention a source of fluid underpressure, a valve between the source and the chamber, and a controllerconnected to the valve and including a sensor connected to the chamberfor determining a pressure therein for operating the valve according toa sensed pressure for maintaining the predetermined pressure in thechamber. The valve includes a pressure-reducing valve and/or aproportional valve. The sensor can be associated with a comparator toestablish upper and lower pressure limits for the valve and operate in afeedback system to maintain the pressure in the chamber substantiallyconstant. A pressure-reducing valve limits the maximum pressure toprevent damage to the workpiece no matter what else occurs.

According to the invention the press further has a second actuatingelement spaced vertically from the other of the dies, a second platencarrying the other die and between the second element and the other die,a second membrane defining a closed chamber having one side operativelybearing vertically on the second platen and an opposite side bearingvertically on the second element. The supply means also pressurizes thesecond membrane.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIG. 1 is a partly diagrammatic vertical section through part of a pressaccording to the invention; and

FIG. 2 is a partly diagrammatic vertical section through a press inaccordance with the invention.

SPECIFIC DESCRIPTION

As seen in FIG. 1 a press 1 according to the invention has a lower die 2typically formed with an array of upwardly open pockets and carried on amassive cast platen 3. An actuating plate or element 5 underneath theplate 3 is vertically reciprocal by an actuator, e.g. a motor orhydraulic cylinder, shown schematically at 4 to open and close the press1. The platen 3 is formed with a downwardly open cavity 13 in which theplate 5 can slide limitedly vertically and bars 11 surrounding thecavity 13 also guide the plate 5 and prevent it from becomingdisconnected in a lowermost position from the platen 3.

According to the invention a flexible and even somewhat elastomericmembrane 7 forming a bladder 10 defining a closed chamber 19 is carriedwith some lateral clearance in the cavity 13. It is connected via a feedline or passage 13 in the platen 3 with a supply conduit 9 connected viaa pressure-limiting valve 12 and a proportional valve 15 with a supply17 of fluid, here air, under relatively high pressure.

FIG. 2, where reference numerals identical to those of FIG. 1 but withprimes are used for structurally and/or functionally identical parts,shows how an upper die 2′ can be carried on a plate 5′ that is fixed asindicated at 18, or that can also be movable by its own actuator.

Both of the supply lines 9 and 9′, in which the fluid pressure isidentical to that in the respective bladders 10 and 10′, are connectedto respective pressure sensors 14 and 14′ in turn connected to acontroller 16 that also operates the valves 12, 12′, 15, and 15′. Thiscontroller 16 therefore maintains a perfectly uniform and relatively lowpressure in both of the bladders 10 and 10′, which can be subdividedinto individually pressurizable compartments as indicated at 19 in FIG.1.

Thus even through the actuator 4 is dimensioned to shift the relativelymassive structure constituted by the die 2, platen 3, and actuatingelement 5 with considerable force, the actual pressure that the dies 2and 2′ will bring to bear on a pair of foils F₁ and F₂ passinghorizontally in steps in a direction D through the press 1 is determinedby the pressure in the bladders 10 and/or 10′. As a result it is notnecessary to provide an extraordinarily sensitive and complex controlsystem for the actuator 4, and it is also not essential to perfectlyalign the dies 2 and 2′ so they close in perfect parallelism. Instead asimple pneumatic pressure-control system limits the pressure the dies 1and 2′ will apply to the workpiece formed by the foils F₁ and F₂.

1. A press comprising: upper and lower dies; an actuating element spacedvertically from one of the dies; a platen carrying the one die andbetween the element and the one die; a membrane defining a closedchamber having one side operatively bearing vertically on the platen andan opposite side bearing vertically on the element; supply means forpressurizing the chamber and maintaining in the chamber a predeterminedpressure; and drive means including an actuator connected to the elementfor vertically displacing the element, platen, and one die.
 2. The pressdefined in claim 1 wherein the platen and element together form acompartment holding the membrane.
 3. The press defined in claim 2wherein the platen is provided with guide bars in which the element isvertically slidable.
 4. The press defined in claim 2 wherein the platenis formed with a cavity open toward the element and holding themembrane.
 5. The press defined in claim 1 wherein the supply meanspressurizes the chamber with a gas.
 6. The press defined in claim 5wherein the membrane forms a bladder.
 7. The press defined in claim 1,further comprising: a source of fluid under pressure; a valve betweenthe source and the chamber; and control means connected to the valve andincluding a sensor connected to the chamber for determining a pressuretherein for operating the valve according to a sensed pressure formaintaining the predetermined pressure in the chamber.
 8. The pressdefined in claim 7 wherein the valve includes a pressure-reducing valve.9. The press defined in claim 7 wherein the valve includes aproportional valve.
 10. The press defined in claim 1 wherein the chamberis subdivided into a plurality of individually controllablecompartments.
 11. The press defined in claim 1, further comprising asecond actuating element spaced vertically from the other of the dies; asecond platen carrying the other die and between the second element andthe other die; and a second membrane defining a closed chamber havingone side operatively bearing vertically on the second platen and anopposite side bearing vertically on the second element, the supply meansalso pressurizing the second membrane.
 12. The press defined in claim 1wherein the supply means maintains in the chamber a substantiallyconstant pressure regardless of a vertical position of the one die andelement.